A Synchronization Control Scheme for Videoconferencing Services

Abstract

<p class="MsoNormal" style="text-align: left; margin: 0cm 0cm 0pt; layout-grid-mode: char; mso-layout-grid-align: none;" align="left"><span class="text"><span style="font-family: ";Arial";,";sans-serif";; font-size: 9pt;">We propose a synchronization control scheme which achieves both speech/video Intra-Stream synchronizations and Inter-Stream synchronization for videoconferencing services over IP networks. The driving principle of our scheme is to guarantee the Intra-Sync speech timing relationships (hence the speech quality) and to adjust the video Intra-Sync and the Inter-Sync accordingly. Towards this aim we use a preventive control for the speech stream and a reactive control for the video stream. More precisely, we use an adaptive playout algorithm that keeps the Intra- Sync constraints within the talkspurts, while the network jitters are compensated by modifying only the silence period lengths on the basis of both speech and video packet delays. We implemented our scheme in a prototype, which allowed us to test the effectiveness of our solution. Actually, we could appreciate both perfect speech intelligibility and very satisfactory user perceived lip-sync. The latter is because the Inter-Sync error is concentrated only at the beginning of the talkspurts, where known experimental tests have shown that it is not detectable.</span></span><span style="font-family: ";Arial";,";sans-serif";; font-size: 9pt;"></span></p

Synchronization Protocol for Real Time Multimedia in Mobile Distributed Systems

“…In the experiment 10 that we present in figure 12 with 10 mobile hosts, the synchronization error at message reception measured by using equation 1, exceeds the maximum permitted of 400 ms in 26% of the messages, this limit is indicated by a horizontal red line. This delay for each message can produce the loss of coherency among the data transmitted in a videoconference [4]. After applying our protocol, the synchronization error measured by using equation 2, is maintained below 400 ms in 99% of transmitted messages.…”

“…For example, in a videoconference the maximum synchronization error permitted between sources is 400 ms [4], while in a more restrictive scenario with an application using video with overlayed text and images the error permitted is 240 ms in order to maintain Quality of Service (QoS) [18]. We define two equations to measure the synchronization error, which are presented below:…”

Measurement Study of Multi-party Video Conferencing

“…The highest bVQM score (the worst video quality) appears at Client 1 (the super node) of Qnext. Generally speaking, all four VC applications do not provide good quality 12 . Because no standard has been set for what level of bVQM score corresponds to what level of perceived quality of a VC service, we have also conducted subjective measurements.…”

“…11 VirtualDub is a video capture and video processing utility for Microsoft Windows. 12 We also objectively measured the audio quality using metric PESQ-LQ (Perceptual Evaluation of Speech Quality-Listening Quality) [6] [8] and found that the PESQ-LQ average score (scale from 1.0 to 4.5, where 4.5 represents an excellent audio quality) is 2.24, 2.68, 3.08 and 3.15 for Mebeam, Qnext, Vsee, and Nefsis, respectively. 13 The threshold for acceptable TV quality corresponds to the MOS value 3.5.…”

Design, Development and Evaluation of an Adaptive and Standardized RTP/RTCP-Based Idms Solution

“…For example, in remote user's speech, the synchronization between the user's audible words and the associated movement of his or her lips is necessary. This is commonly known as lip synchronization or lip-sync (e.g., [Che03] and [Bar07]). A similar inter-media synchronization scenario is when using a two-lens stereo camera system with an internal mono microphone.…”